1. Field of the Invention
This application relates to a re-keyable cylinder lock, more particularly to an improvement that provides a re-keyable cylinder lock with a limit unit inserted into one of a plurality of radial holes located at a predetermined depth of a key hole.
2. Description of the Related Art
Re-keyable cylinder locks are well known in the art. Examples of the re-keyable cylinder locks are disclosed in U.S. Pat. Nos. 6,862,909 and 6,871,520. Such cylinder locks can be re-keyed using a new replacement key to replace an old key, without disassembling components of the cylinder locks. A method of re-keying includes inserting the replacement key into a key hole in the cylinder lock after the old key inserted therein is pulled out of the key hole. The insertion of the replacement key repositions tumbler pieces of the cylinder lock relative to a key bit of the replacement key so that orientations of the tumbler pieces are changed.
For re-keying, it is necessary that the key bit of the replacement key inserted into the key hole must reach a predetermined depth of the key hole. Otherwise, the tumbler pieces cannot be entirely re-oriented, and the re-keying cannot be completed. In case of incomplete re-keying, all steps of the re-keying have to be repeated, which is very inconveniences. A solution to the problem of incomplete re-keying is therefore desirable.
On the other hand, it is known to provide a re-keyable cylinder lock with a re-keying unit that can engage tumbler pieces so as to position the same in a pre-determined orientation and that can disengage from the tumbler pieces to permit the tumbler pieces to change in position so as to match a replacement key. When the re-keying unit engages the tumbler pieces, the cylinder lock cannot be re-keyed, but can be placed in a locking position using a valid key to lock a plug of the cylinder lock against rotation so that a door can be locked. When the re-keying unit disengages from the tumbler pieces, the cylinder lock can be re-keyed using a replacement key to change the orientation of the tumbler pieces. At this state, the plug can be rotated, but cannot be prevented from rotation.